“If we can convince policy makers that this is a public health opportunity, we can build well-designed communities, and in the long term you have made a big difference in health outcomes,” its co-author Chinmoy Sarkar told the Thomson Reuters Foundation. “With evidence, we can plan multi-functional, attractive neighbourhoods that promote physical activity, promote social interaction, and shield from negatives such as pollution and feeling unsafe.”

Actually, when you read the study, it appears to say a lot less than that headline does, and looks at only at the “association between adiposity outcomes and residential density,” the relationship between obesity and residential density, finding an inverse relationship: the higher the urban density, the skinnier the residents. They then note that obesity is a risk factor for diabetes, cardiovascular disease and cancer. They do not get into the other risk factors that exist in the city, like air quality, nor do they ever actually correlate it with happiness.

But for that one key metric, density vs obesity, they do find a key turning point -- 1800 units per square kilometre or, by my calculation, 4663 units per square mile. (I attached a chart of US city densities for comparison below.) The study authors conclude:

In view of the potentially significant benefits of healthy density environments on weight outcomes, understanding underlying pathways merits further investigation for effective policy making. First, high residential density is synonymous with compactness, greater access to destinations, and walkability, and thus active travel. Positive associations with healthy weight have been reported for walkability and active commuting… Second, a highly compact dense residential environment might act as a proxy for enhanced community social capital and support. The intangible stress-relieving potential of centrality, accessibility, and social capital needs to be further examined in view of their protective effects on obesity.

It seems absurd. Everyone knows, because we have been told so often that the inner cities teem with desperate, exhausted people who have nowhere else to go, surviving in crowds, stress, dirt and the endless, cacophonous demands of consumerism, eyes for ever downcast in fear that some witless bumpkin might misadvisedly hazard a breezy “good morning”.

But then she notes that in the city, there are lots of places to walk, including, these days, political demonstrations.

In the city, there is so much to walk to: art fairs, outdoor screenings of much-loved films, new areas to explore, demos. You can go on a demo every day of the week. These tend to involve a good deal of walking and hanging out with like-minded pals. That’s a sobering thought. We city dwellers would be a good deal less healthy and happy if we didn’t have such large numbers of things to protest against.

Both articles in the Guardian seem to read a lot more into this study than is actually there, and as noted in related links below, we have been saying much the same in TreeHugger for years. But it is reassuring to see a study that confirms it: walkable cities keep you thin. You, like the Guardian, can infer the rest.